Document Type

Technical Report

Publication Date



Calcite deposits, composed of a mixture of calcium carbonate and silicon dioxide, were found in fractures and small cavities within the welded tuff of Yucca Mountain. This research investigation involves determining the presence of thermophilic, calciumprecipitating bacteria within these deposits. The possible existence of thermophilic bacteria may help to resolve the issue of whether these calcite deposits formed from precipitation of dissolved calcium carbonate in rain water transported from the overlying soil environment or as a result of upwelling of geothermally-heated waters transported from below the mountain. Evidence for microbially-influenced calcite precipitation in these deposits is indicated by the presence of moderately-thermophilic, calciumprecipitating bacteria. Growth of bacteria enriched from crushed calcite and calcite/tuff mixed samples collected from tunnels within Yucca Mountain indicate a tendency for thermophiles to be found in calcite deposits and mixed rock samples compared to tuff samples (no calcite) which lacked bacterial growth at temperatures of 50° C and higher. Calcite isolates growing at 60 and 70° C were identified as thermophiles, the most common identification being Bacillus stearothermophilus. SEM and electron dispersion spectroscopy (EDS) results showed that bacteria, isolated from Yucca Mountain calcite and calcite/tuff, produced calcite (CaCO3) when grown on calcium-enriched medium. This evidence indicates a possible warm water influence in the history of Yucca Mountain.


Bacillus stearothermophilus; Calcite; Groundwater – Temperature; Nevada – Yucca Mountain; Thermophilic bacteria


Bacteriology | Environmental Microbiology and Microbial Ecology | Hydrology | Microbiology




Document ID: TR-03-004 Revision 0
Prepared for the U.S. DOE/UCCSN Cooperative Agreement
Number DE-FC08-98NV 12081
Task 22
Signatures have been redacted for privacy and security measures.